This invention relates to the technology of image recording apparatus using a long line head. More particularly, the invention relates to a head position detecting method which detects the relative positions of adjacent short heads in order to record high-quality image using a line head comprising an array of such short heads. The invention also relates to an image recording apparatus which implements the detecting method and a storage medium loaded with a program for implementing the detecting method.
The invention further relates to a recording head in which data representing the relationship among the relative positions detected by the detecting method is stored and an image recording apparatus provided with the recording head as well as a storage medium which is loaded with a program for implementing the sequence of determining the driving timing of each short head by using the data stored in the recording head.
Unexamined Published Japanese Patent Application (JPA) Nos. 9622/1973 and 51837/1979 teach ink-jet recording apparatus of a type in which part of ink is rapidly evaporated by impulse heating so that the resulting force of expansion allows ink drops to be propelled from orifices.
JPA Nos. 50601/1993 and 207956/1999 teach ink-jet recording apparatus of another type in which a diaphragm is provided in an ink chamber and vibrated by static electricity, with a piezoelectric device or otherwise so that ink drops are propelled from nozzles.
These and other types of ink-jet recording apparatus have many advantages such as fairly low price, ease in handling and good image quality and hence are used extensively as printers in various applications.
In such ink-jet printers and various other printers that employ a xe2x80x9crecording headxe2x80x9d as in thermal printers and dot impact printers, the recording head is usually a short one comprising an array of recording elements and the recording medium at rest is scanned by the recording head which is moved by a carriage in a direction perpendicular to the direction of arrangement of the recording elements and when one scan cycle ends, the recording medium is moved in the direction of arrangement of the recording elements over the distance determined by the number of recording elements in the head and another scan is performed by the same procedure as described above; this process is repeated to record image on the entire surface of the recording medium.
Printers are also known that use a so-called xe2x80x9cline headxe2x80x9d which has recording elements arranged over a distance to cover the entire length of one side of the recording medium. The major advantage of using the line head is that by merely performing relative movements of the recording medium and the line head in an auxiliary direction perpendicular to the direction of arrangement of the recording elements, the entire region of the recording medium can be scanned with the recording elements to record image on the entire surface of the recording medium. As a result, printers using the line head can accomplish image recording rapidly and by simple operations without movement of the carriage and intermittent transfer of the recording medium.
On the other hand, the line head has several disadvantages such as higher cost, lower yield and reliability than the short head. In addition, if some of the recording elements break, the expensive line head has to be replaced as a unit and this results in high repair cost.
In order to solve these problems of the line head, it has been proposed that a plurality of short heads each having recording elements arranged in one direction (a main scanning direction) be arranged in the main scanning direction [see Examined Japanese Patent Publication (JPB) No. 38589/1992]. The advantages of short heads such as low cost, high yield and reliability are retained by this line head. In addition, if some recording elements break, only the short head having such broken recording elements need be replaced and this contributes to considerable economy in terms of repair cost.
On the other hand, in order to ensure that high-quality image without defects such as streaks (streaky unevenness in density) and clear spots is recorded with the line head comprising an array of short heads, the individual short heads must be positioned exactly enough to give an appropriate or equal pitch of recording elements at each of the joints between adjacent short heads. It goes without saying that the ends of adjacent two short heads which form the joint therebetween need be produced in an extremely precise manner so that the short heads can be positioned exactly. However, the recording elements are arranged at such small intervals (e.g. on a pitch of 20 xcexcm if the resolution is 1200 dpi) that difficulty is found in arranging many short heads in exact registry in terms of making the end of each short head which forms a joint with that of the adjacent short head, and considerable difficulty is involved in positioning.
In another approach, adjacent short heads may be shifted in the auxiliary scanning direction such that the recording elements near the end of one short head overlap those near the end of the other short head in the main scanning direction. This approach facilitates making the end of each short head which forms a joint with that of the adjacent short head.
However, to know the position of the joint between the adjacent short heads correctly so that the pitch of recording elements (in the main scanning direction) is made equal even in the joint, the appropriate measuring instrument is necessary and after the replacement of some short heads, it is difficult for the user to pinpoint the joint positions.
Further, in order that printing (dot generation) by means of recording elements of individual short heads making up a long line head can be made on one line in the main scanning direction, positional offsets in the auxiliary scanning direction among the recording elements of the individual short heads must be understood exactly.
However, also in this case, the appropriate measuring instrument is necessary to know the positional offsets in the auxiliary scanning direction exactly, and after the replacement of some short heads, it is also difficult for the user to pinpoint the joint positions.
The present invention has been accomplished under these circumstances and has as a first object providing a head position detecting method that can be applied to a long line head consisting of a plurality of short heads each comprising a unidirectional array of recording elements and by which the relative positions of the recording elements in adjacent short heads (in the main and auxiliary scanning directions), namely, the position of the joint between the short heads (in the main and auxiliary scanning directions) can be detected correctly without using any sophisticated measuring instruments, thereby ensuring that high-quality image having no streaks (unevenness in density) or clear spots can be recorded by means of the long line head, an image recording apparatus which implements the head position detecting method, and a storage medium loaded with software for implementing the position detecting method.
In addition to the first object mentioned above, a second object of the present invention is to provide a recording head in which data representing the relationship among the relative positions detected by the detecting method is stored and an image recording apparatus provided with the recording head as well as a storage medium which is loaded with a program for implementing the sequence of determining the driving timing of each short head by using the data stored in the recording head.
The inventors of the present invention have conducted intensive studies with a view to attaining the first and second objects mentioned above, and found that adjacent short heads are positioned in particular such that the recording elements near the end of one short head overlap those near the end of the other short head in the main scanning direction and selected recording elements are driven in the overlapping area and, if necessary, density adjustment is also performed, for example, by image processing (video signal processing) so as to prevent the deterioration of image quality due, for example, to excessive packing of recording elements in the overlapping area or the error in the pitch of recording elements, thereby providing ease in the registering of short heads.
Subsequently, the inventors of the present invention have also found that the finding as mentioned above requires correctly knowing the relative positions of the recording elements in adjacent short heads (in the main and auxiliary scanning directions), namely, the positions of the recording elements in the joints (in the main and auxiliary scanning directions), but that the relative positions of the recording elements in the main and auxiliary scanning direction can be correctly known by actually printing on a recording medium using the recording elements in each joint between adjacent short heads and preferably by actually printing while properly controlling the recording elements in each joint, whereupon, for example, even after the replacement of some short heads, the user can pinpoint the joint positions. The inventors have thus completed the present invention.
In order to attain the first object described above, the first aspect of the present invention provides a head position detecting method applicable to recording with a line head comprising a plurality of short heads that each have at least one unidirectional array of recording elements and which are arranged in a direction of arrangement of the recording elements, comprising the steps of: making relative movements of the line head and a recording medium in a direction perpendicular to the direction of arrangement of the recording elements as at least one pair of first and second short heads adjacent to each other which constitute the line head are operated to perform first recording with at least one recording element on an adjacent side of the first short head and second recording with at least one recording element on an adjacent side of the second short head, thereby obtaining a first recording pattern; and detecting, from the first recording pattern obtained, relative first positions of the first and second short heads adjacent to each other in the direction of arrangement of the recording elements.
It is preferable that the head position detecting method of the first aspect further comprises the steps of: performing the first recording with the first short head by using a plurality of recording elements on the adjacent side of the first short head, and the second recording with the second short head by using a plurality of recording elements on the adjacent side of the second short head, thereby obtaining a second recording pattern; and detecting, from the second recording pattern obtained, second positions of the first and second short heads adjacent to each other in a direction approximately perpendicular to the direction of arrangement of the recording elements.
In order to attain the first object described above, the second aspect of the present invention provides a head position detecting method applicable to recording with a line head comprising a plurality of short heads that each have at least one unidirectional array of recording elements and which are arranged in a direction of arrangement of the recording elements, comprising the steps of: making relative movements of the line head and a recording medium in a direction perpendicular to the direction of arrangement of the recording elements as at least one pair of first and second short heads adjacent to each other which constitute the line head are operated to perform first recording with a plurality of recording elements on an adjacent side of the first short head and second recording with a plurality of recording elements on an adjacent side of the second short head, thereby obtaining a second recording pattern; and detecting, from the second recording pattern obtained, second positions of the first and second short heads adjacent to each other in a direction approximately perpendicular to the direction of arrangement of the recording elements.
In the head position detecting method of the present invention, the first recording with the first short head and the second recording with the second short head are preferably performed in adjacent areas that differ in a direction perpendicular to the direction of arrangement of the recording elements.
Preferably, the first recording with the first short head and the second recording with the second short head are performed in identical positions in a direction perpendicular to the direction of arrangement of the recording elements.
Preferably, every n-th recording element is operated to perform the second recording with the second short head, n being an integer of at least two.
Preferably, operative recording elements are successively changed in the second recording with the second short head.
In order to attain the second object described above, the third aspect of the present invention provides a recording head which is a line head including a plurality of short heads that each have at least one unidirectional array of recording elements and which are arranged in a direction of arrangement of the recording elements, comprising: a memory for storing data representing a relationship between second positions as obtained by the steps of: making relative movements of the line head and a recording medium in a direction perpendicular to the direction of arrangement of the recording elements as at least one pair of first and second short heads adjacent to each other which constitute the line head are operated to perform first recording with a plurality of recording elements on an adjacent side of the first short head and second recording with a plurality of recording elements on an adjacent side of the second short head, thereby obtaining a second recording pattern; and detecting, from the second recording pattern obtained, the second positions of the first and second short heads adjacent to each other in a direction approximately perpendicular to the direction of arrangement of the recording elements.
Preferably, the data representing the relationship between the second positions is data on a distance between the first and second short heads adjacent to each other.
Preferably, the data representing the relationship between the second positions is data on a difference in driving timing between the first and second short heads adjacent to each other under predetermined recording conditions.
In order to attain the second object described above, the fourth aspect of the present invention provides an image recording apparatus comprising: a line head including a plurality of short heads that each have at least one unidirectional array of recording elements and which are arranged in a direction of arrangement of the recording elements; a scanner for making relative movements of the line head and a recording medium in a direction perpendicular to the direction of arrangement of the recording elements; a recording control device by which during the relative movements by the scanner, at least one pair of first and second short heads adjacent to each other constituting the line head are operated to perform first recording with a plurality of recording elements on an adjacent side of the first short head and second recording with a plurality of recording elements on an adjacent side of the second short head, whereby a second recording pattern for use in detecting second positions of the first and second short heads adjacent to each other in a direction approximately perpendicular to the direction of arrangement of the recording elements is obtained; a memory for storing data representing a relationship between the second positions that were detected from the second recording pattern obtained by the recording control device; and a timing determining device for determining a driving timing for each short head by using the data representing the relationship between the second positions stored in the memory; wherein the recording control device drives the plurality of short heads at the driving timing determined by the timing determining device when the scanner moves the recording medium relatively.
In order to attain the first object described above, the fifth aspect of the present invention provides an image recording apparatus comprising: a line head comprising a plurality of short heads that each have at least one unidirectional array of recording elements and which are arranged in a direction of arrangement of the recording elements; a scanner for making relative movements of the line head and a recording medium in a direction perpendicular to the direction of arrangement of the recording elements; and a recording control device by which during the relative movements by the scanner, at least one pair of first and second short heads adjacent to each other constituting the line head are operated to perform first recording with at least one recording element on an adjacent side of the first short head and second recording with at least one recording element on an adjacent side of the second short head, whereby a first recording pattern for use in detecting relative first positions of the first and second short heads adjacent to each other is obtained.
Preferably, in order to obtain a second recording pattern for use in detecting second positions of the first and second short heads adjacent to each other in a direction approximately perpendicular to the direction of arrangement of the recording elements, the recording control device further performs: the first recording with the first short head by using a plurality of recording elements on the adjacent side of the first short head; and the second recording with the second short head by using a plurality of recording elements on the adjacent side of the second short head.
It is preferable that the image recording apparatus of the fifth aspect further includes a memory which is incorporated into the line head and stores data representing a relationship between the second positions of the first and second short heads adjacent to each other in a direction approximately perpendicular to the direction of arrangement of the recording elements, as detected from the second recording pattern obtained by the recording control device.
In order to attain the first object described above, the fifth aspect of the present invention provides a computer-accessible storage medium for executing an image recording sequence with a line head comprising a plurality of short heads that each have at least one unidirectional array of recording elements and which are arranged in a direction of arrangement of the recording elements, the medium being loaded with a program for executing a first image recording sequence according to which the line head and a recording medium are moved relatively in a direction perpendicular to the direction of arrangement of the recording elements as at least one pair of first and second short heads adjacent to each other constituting the line head are operated to perform first recording with at least one recording element on an adjacent side of the first short head and second recording with at least one recording element on an adjacent side of the second short head, whereby a first recording pattern for use in detecting relative first positions of the first and second short heads adjacent to each other is obtained.
Preferably, the program further executes a second image recording sequence according to which the first recording with the first short head is performed by using a plurality of recording elements on the adjacent side of the first short head, and the second recording with the second short head is performed by using a plurality of recording elements on the adjacent side of the second short head, whereby a second recording pattern for use in detecting second positions of the first and second short heads adjacent to each other in a direction approximately perpendicular to the direction of arrangement of the recording elements is obtained.
In order to attain the second object described above, the seventh aspect of the present invention provides a computer-accessible storage medium which is loaded with a program for executing a sequence of determining a driving timing of each short head by using data representing a relationship between second positions stored in a memory of a recording head when image recording is performed with the recording head which is a line head including a plurality of short heads each having at least one unidirectional array of recording elements and being arranged in a direction of arrangement of the recording elements, and in which the memory previously stores the data representing the relationship between the second positions as obtained by the steps of: making relative movements of the line head and a recording medium in a direction perpendicular to the direction of arrangement of the recording elements as at least one pair of first and second short heads adjacent to each other which constitute the line head are operated to perform first recording with a plurality of recording elements on an adjacent side of the first short head and second recording with a plurality of recording elements on an adjacent side of the second short head, thereby obtaining a second recording pattern; and detecting, from the second recording pattern obtained, the second positions of the first and second short heads adjacent to each other in a direction approximately perpendicular to the direction of arrangement of the recording elements.